You've worked really hard this year and accomplished a ton. It's only September, but you've already met or exceeded all your goals for the year. You deserve a raise and were planning to ask for one when you had your annual performance review in December. That's way too late. You have until September 30 to make sure your boss knows why you deserve a huge bump in pay come January 1.
Lots of companies do an annual year end increase, and if your company does, you need to start talking with your manager now if you want more than an average increase. Why? Because raises don't happen overnight and they don't happen in a vacuum. For many companies, that process takes the entire 4th quarter, which is why you need to make your case before October 1. Here's what (probably) happens in your company for annual increases:
The CEO, CFO, and other executives determine a budget for that year. They may base it on an absolute dollar amount or they may base it on a percentage of the current salary budget. Regardless, that's the budget that exists and your manager can't go outside this budget (unless you report to the CEO, then all bets are off). The further down the food chain you are, the more your boss is bound by this budget.
The money needs to be divided fairly. You are totally awesome, but so are your co-workers, Bob and Karen. Your manager has been given 3 percent of departmental salaries to use for raises. So, if you, Bob, and Karen are all outstanding, everyone's raises can't amount to more than 3 percent. If your boss gives you a 9 percent raise, Bob and Karen get nothing. (Assuming your salaries are identical.)
The raises need to be approved. Let's say you, Bob, and Karen really are amazing, and so your boss says 4 percent all around. She then has to send that to her boss, who then says, Nope, not only can you not go over your 3 percent budget, but I think that this other department deserves a better raise, so I'm knocking your group to 2.5 percent so that the other group can get bigger raises!
At this point, your manager has to make her case for why her group deserves extra money. She needs to be prepared--she won't win if she just says "but my group is awesome!"
It's too late to make changes at your performance review. When you sit down with your boss for your annual performance review, your boss has already determined your raise and it's been approved by all levels. So when she says, "Great job! 2.5 percent increase!" there's very little you can say to get that changed. Remember, you don't just have to convince her, you have to convince practically the entire leadership team because all the money has been allocated. Your boss can't yank back someone else's raise at this point, just because you've made an incredibly good argument for a larger increase.
Prepare now and meet with your manager before the end of September. Why do you deserve a big raise, or even a growth promotion? Go and make your argument now. Now is when your boss can decide to reward your efforts. It's far easier to find extra money for you at the beginning of the year end salary increase process than it is at the end.
Document your successes. Demonstrate how the company is better off because of what you've done. Show how you've gone above and beyond. Don't assume that your boss will be fair because she's a good boss. She may be awesome but make your case anyway. Most managers (even great ones) are not fully aware of everything you've done. Remember, they know less about the great employees because you take care of things on your own. So, speak up now!
Budgets are always going to limit the raise you'll receive, but by making your case early, your manager will have the best chance of getting permission to give you the best raise possible.